Catalytic cracking processes are conventionally employed to produce gasoline and light distillate fractions from heavier hydrocarbon feed stocks. Deterioration occurs in the cracking ability of the catalyst attributable to the deposition on the catalyst of metals contained within the charge stock. The deposition of these metals such as nickel and vanadium results in the decrease in production of the gasoline fraction. Additionally, the effect of these contaminant metals when deposited on the catalytic cracking catalyst is to increase coke production and to increase cracking depth as shown by the increase in hydrogen production.
The cracking catalysts to which the method of this invention is applicable are those conventionally employed in the cracking of hydrocarbons boiling substantially above 600.degree.F. (316.degree.C) for the production of motor fuel blending components and light distillates. These catalysts generally contain silica or silica-alumina, such materials frequently being associated with zeolitic materials. These zeolitic materials could be natural occurring or could have been produced by conventional ion exchange methods so as to provide metallic ions which improve the activity of the catalyst. The invention is particularly applicable to molecular sieve zeolitic-modified silica-alumina catalysts.
Examples of cracking catalysts to which the method of this invention is applicable include hydrocarbon cracking catalysts obtained by admixing an inorganic oxide gel with an aluminosilicate and aluminosilicate compositions which are strongly acidic in character as a result of treatment with a fluid medium containing at least one rare earth metal cation and a hydrogen ion or ion capable of conversion to a hydrogen ion. Other cracking catalyst compositions of this invention include those crystalline aluminosilicate zeolites having the mordenite crystal structure.